A rotor for a synchronous motor, which includes a plurality of permanent magnets radially arranged around a rotating shaft, and a plurality of laminated core members arranged around the rotating shaft so as to hold each magnet between the core members in a circumferential direction and so as to form magnetic poles, has already been known. In such rotor, the permanent magnets and the laminated core members are generally supported as follows: annular end plates are fixed to the rotating shaft and arranged at the axial both ends of the permanent magnets and the laminated core members, each laminated core member is fixedly held in the rotor by a rod member which extends through the core member and is connected to the end plates at both ends of the rod member, and then, each permanent magnet is positioned and fixedly supported in a radial direction by outer and inner hooks which are formed respectively at outer and inner periphery of side surfaces of adjacent laminated core members.
When the rotor having such a structure is used for a high-speed synchronous motor or a high-torque synchronous motor formed by axially connecting the rotors to one another, the rotating shaft and the rod members may be radially outwardly bent by centrifugal force or bending torque caused by reaction of an object to be driven. As a result, the balance of a rotor is deteriorated and the distance between the outer circumferential surfaces of the laminated core members and the inner circumferential surfaces of a stator surrounding the rotor is varied, possibly causing a cogging torque to be generated and the laminated core members to be brought into contact with the stator.
A solution has been provided such that a reinforcing member, used for preventing the rod members from being bent by external force, is incorporated into, e.g., the rotor for a high-torque synchronous motor. An example of this kind of rotor is illustrated in FIGS. 6a and 6b. The rotor includes two core assemblies 2 axially adjacent to each other and fixed to a common rotating shaft 1. Each core assembly 2 has a plurality of permanent magnets 3 and laminated core members 4. Rod members 5 extend successively through the laminated core members of both core assemblies 2, and are connected to end plates 6 at the each end of the rod members. Disc member 7 including a shaft hole, into which the rotating shaft 1 is inserted, and rod supporting holes, into which the rod members 5 are inserted, is arranged between the core assemblies 2. Each laminated core member 4 is provided with an outer hook 8 and an inner hook 9 for supporting the permanent magnet 3. The circular-plate member 7 is a reinforcing member for fixedly and mechanically retaining the rod members 5 against external force, and thus maintaining the rigidity of the rotor.
In the above-mentioned conventional rotor, the outer peripheral surface of each laminated core member is formed bulgingly along a predetermined arc, so that the magnetic flux in the gap between the inner peripheral surface of a stator and the outer peripheral surface is distributed in a sinusoidal curve relative to a rotation angle. Therefore, in the case where a small number of the magnetic poles or laminated core members is used, or where the thickness of the permanent magnets is small, idealizing the arc form of the outer peripheral surface of the laminated core member may mean that the outer peripheral surface of the permanent magnet cannot be covered with the distal end of the arc, and thus making it difficult to form the outer hook. In the above-mentioned conventional rotor, however, the fixing of the permanent magnets particularly in a radial direction depends on the outer hooks provided to the laminated core members. Consequently, in this case, in order to ensure the structural reliability of the rotor, the outer hooks are formed more or less at the sacrifice of obtaining the ideal sinusoidal-curve distribution of the magnetic flux. Such a formation of the outer hooks deteriorates the rotor performance by, e.g., a cogging torque.